Heretofore, the present inventors have invented a blood flow speed measurement apparatus which applies laser light to a biotissue having blood cells such as the eyeground or the skin; leads a so-called speckle image (an image of random speckle pattern formed as a result of interference of reflection light from the blood cells) to an image sensor such as a solid state imaging device (CCD or CMOS); successively captures and stores a large number of speckle images at predetermined intervals; selects a predetermined number of images from the large number of stored images; calculates a value which reflects the speed of a time course change in the output of each pixel throughout the images; and calculates the speed of blood cells (blood flow speed) from the calculated value. In a blood flow speed measurement apparatus of such a type, since the value indicating the output changing speed of each pixel corresponds to the moving speed of blood cells, the blood flow distribution in the biotissue can be color-disposed on a monitor screen as a two-dimensional image (a blood flow map) on the basis of the calculated value indicating the output changing speed of each pixel. A blood flow map observed in actuality is composed of a series of blood flow maps (hereinafter also referred to as “original maps”) calculated at a speed of about 30 frames per sec, and can be displayed as a motion video. Therefore, the invented apparatus has been put to practical use as an apparatus for observing the haemodynamics of the eyeground or skin (see Patent Documents 1 to 6).
Also, the present inventors have proposed a blood flow speed imaging apparatus (see Patent Document 7). In this apparatus, a series of blood flow maps obtained through blood flow measurement performed for several seconds are used, and a change in blood flow appearing periodically in synchronism with the heartbeat is analyzed in various regions within a field of observation view. A numerical value (i.e., the degree of distortion) is introduced so as to distinguish between a region having a sharp rising waveform attributable to the arterial blood flow and a region having a mildly rising and falling waveform attributable to the venous blood flow. Thus, the apparatus can display on the blood flow maps pulsations caused by the arterial blood flow and pulsations caused by the venous blood flow.
Moreover, the present inventors has proposed the following method. A new blood flow image diagnosing function is added to the conventional apparatus, and a function is added to a computation section so as to separate, from data of a plurality of blood flow maps over one or more heartbeats, a blood flow within a surface blood vessel within an observation region of a biotissue and the background blood flow therearound. These blood flows are displayed on the blood flow map on a display section in a distinguishable manner. Various variables which characterize the blood flow waveforms of the separated regions are defined, and these variables are compared for clinical diagnosis. In the following description, an apparatus having such a function added thereto will be referred to as a “blood flow image diagnosing device.”